Comparative studies of MCs+-SIMS and e?-beam SNMS for quantitative analysis of bulk materials and layered structures

For the quantification of heterostructure depth profiles the knowledge of relative sensitivity factors (RSF) and the influence of matrix effects on the measured profiles is necessary. Matrix dependencies of the measured ion intensities have been investigated for sputtered neutral mass spectrometry (SNMS) and MCs⁺-SIMS. The use of Cs as primary ions for SNMS is advantageous compared to Ar because the depth resolution is improved without changing RSFs determined under Ar bombardment. No significant amount of molecules has been found in the SNMS spectra under Cs bombardment. Using MCs⁺-SIMS the RSFs are matrix dependent. An improvement of depth resolution can be achieved by biasing the sample against the primary ion beam for SNMS due to a reduction of the net energy of the primary ions and a resulting more gracing impact angle.     

SIMS depth profile analysis using MCs+ molecular ions

Summary The use of Cs⁺ primary ions in conjunction with the detection of MCs⁺ molecular ions (where M is the element to be monitored) in SIMS depth profiling is shown to be an efficient method of minimizing the variations of ion yields with sample composition, e.g., at the interface of multilayer structures. Depth profiles of several such samples demonstrate that MCs⁺ intensities follow closely the concentrations of the respective elements, providing the possibility of a (semi)quantitative analysis of major components by means of secondary ion mass spectrometry. As indicated by the similarity of their energy distribution data, the formation and emission process of MCs⁺ molecules seems coupled to that of Cs⁺ ions.     

MCs+ secondary ion and sputtering yields of oxygen-exposed semiconductors and glasses

The emission of MCs⁺ molecular ions sputtered by Cs⁺ ion impact from a variety of elemental (Si and Ge) and compound (GaAs, InP, InSb, ZnSe, CdS, CdSe, CdTe and CdZnTe) semiconductors and a selection of glass samples of different composition has been investigated. For the glass samples a set of relative sensitivity factors has been determined which are largely composition-independent and provide the possibility of a reliable quantification of glasses by MCs⁺ SIMS. For the semiconductors fractional ion yields (i.e. the number of detected MCs⁺ ions per sputtered M atom) range from 10^–6 to some 10^–4 and exhibit little variation with the oxygen surface coverage of the specimen. Depending on M, the emission of MOCs⁺ molecular species becomes prominent (or even dominating) at high oxygen concentrations. Furthermore, total sputtering yields for 5.5 keV Cs⁺ impact and different oxygen partial pressures have been determined from sputtered craters.     

Quantitative surface analysis of coated materials by SNMS

A great number of coating techniques and coating materials have been developed and are in practical use. To meet all requirements in quality of technical coating systems methods of quality control and quality assurance are essential. In connection with the production of coated steel secondary neutral mass spectrometry (SNMS) can be looked upon as a new tool for further approach.The investigations reported started with the determination of sputter erosion rates and experiments with calibration standards produced by vacuum coating.For the quantification of SNMS signals the relative sensitivity factors of all elements in question must be known. The use of complex composed reference materials for this purpose may lead to wrong results. That is due to matrix effects and occurs also for the determination of sensitivity factors for elements at low contents. Therefore the production of reference materials by pressing of metallic and oxidic powders was proposed and tested. The experiments described have proved the applicability of pressed samples for the determination of sensitivity factors, for the investigation of oxides, nitrides and carbides, and for the analysis of chips and dusts by SNMS.Dedicated to Professor Günther Tölg on the occasion of his 60th birthday     

Quantitative depth profile analysis of high-Tc-superconductors with sputtered neutral mass spectrometry (SNMS)

Summary SNMS, a new surface sensitive as well as a bulk analysis technique, has been applied to the quantitative compositional depth profiling analysis of conductive and insulating thin films. Its performance is demonstrated by investigation of YBCO superconductor bulk analysis and sputter deposited layers on single crystalline substrates of SrTiO₃ and Al₂O₃. A stable stoichiometric volume has been observed in bulk material and thin films respectively. Inside a range of 500 nm from the surface, the composition deviates strongly from the stoichiometric concentration of Y and Ba. Comparative measurements with a freshly cleaved piece of YBCO bulk material which was immediately loaded into the ultrahigh vacuum analysis chamber show constant and stoichiometric concentration of all faced elements (Y, Ba, Cu, O) from the beginning of surface etching. The ratio of Y to Ba and Cu varied by less than 2%, the ratio Cu to oxygen by less than 5% from the nominal composition 1-2-3 (4).

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Quantitative Tiefenprofilanalyse von HT_c-Supraleitern mit SNMS

     

Examinations regarding the correctness of quantitative surface analysis using SNMS

Summary For the assessment of the correctness of depth profile analyses with non-ideal technical metal surfaces using secondary neutral particle mass spectrometry (SNMS), the roughness of the sample surface was examined for the transition width of the signal. It is shown that with elements with low sputter rates (Al Mn), similar to that of the substrate element (Fe), there is no significant influence of the roughness. However, clear dependencies are observed for tin and zinc, elements with high sputter rates. Whereas tin gave acceptable results when the roughness was significant, cone formation was observed with zinc which caused abnormal sputter behaviour. The use of high-frequency sputter processes eliminates this cone formation and leads to constant signals, even with thick zinc layers. This method is therefore not only suitable for use with non-conductors, as originally planned, but also offers considerable advantages in the analysis of metal coatings.     

Analysis of sputter deposited and evaporated tantalum oxide layers on SiO2 by SNMS, XPS, TDS and TRFA

Summary Tantalum oxide films with a thickness of 100 nm for the application in high power laser systems have been prepared on SiO₂-substrates by ion beam sputtering or electron beam evaporation. Comparative analysis of both groups of dielectric films has been performed with the separate bombardment mode of secondary neutral mass spectrometry SNMS, X-ray induced photoelectron spectroscopy XPS, thermal desorption spectroscopy TDS and total reflection X-ray fluorescence analysis TRFA.

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Analyse von aufgesputterten und aufgedampften Tantaloxid-Schichten auf SiO₂ mit Hilfe von SNMS, XPS, TDS und TRFA

     

Quantitative determination of element distributions in silicon based thin film solar cells using SNMS

The determination of elemental distributions in thin film solar cells based on amorphous silicon using electron beam SNMS is possible by quantifying the measured ion intensities. The relative sensitivity factors (RSFs) for all elements measured have to be known. The RSFs have been determined experimentally using implantation and bulk standards with known concentrations of the interesting elements. The measured RSFs have been compared with calculated RSFs. The model used for the calculation of the RSFs takes into account the probability for electron impact ionization and the dwell time of the neutrals inside the postionization region. The comparison between measured and calculated RSF shows, that this model is capable to explain the RSFs for most elements. Differences between calculated and measured values can be explained by the formation of hydride and fluoride molecules (in case of H and F) and influences of the angular distribution of the sputtered neutrals in case of Al. The experimentally determined RSFs have been used for a quantification of depth profiles of the i-, buffer-, p- and front contact layers of a-Si solar cells.     

Quantitative determination of element distributions in silicon based thin film solar cells using SNMS

The determination of elemental distributions in thin film solar cells based on amorphous silicon using electron beam SNMS is possible by quantifying the measured ion intensities. The relative sensitivity factors (RSFs) for all elements measured have to be known. The RSFs have been determined experimentally using implantation and bulk standards with known concentrations of the interesting elements. The measured RSFs have been compared with calculated RSFs. The model used for the calculation of the RSFs takes into account the probability for electron impact ionization and the dwell time of the neutrals inside the postionization region. The comparison between measured and calculated RSF shows, that this model is capable to explain the RSFs for most elements. Differences between calculated and measured values can be explained by the formation of hydride and fluoride molecules (in case of H and F) and influences of the angular distribution of the sputtered neutrals in case of Al. The experimentally determined RSFs have been used for a quantification of depth profiles of the i-, buffer-, p- and front contact layers of a-Si solar cells.     

Depth profile analysis of thin film solar cells using SNMS and SIMS

SNMS (sputtered neutrals mass spectrometry) and SIMS (secondary ion mass spectrometry) are used for the depth profile analysis of thin film solar cells based on amorphous silicon. In order to enhance depth resolution, model systems are analyzed only representing parts of the layered system. Results concerning the TCO (transparent conducting oxide)/p interface and the n/i interface are presented. To minimize matrix effects, SNMS is used when the sample consists of layers with different matrices. Examples are the TCO/p interface (where the transition lengths of the depth profiles are found to be sharper when ZnO is used as TCO compared to SnO₂) and SnO₂/ZnO interfaces in coated TCO layers (where a Sn contamination inside the ZnO layer is found depending on the plasma pressure during the ZnO deposition). SIMS is used when the limits of detection reached by SNMS are not sufficient. Examples are H depth profiles in ZnO layers or P depth profiles near the n/i-interface.     

Investigation of Al diffusion in different oxide thin-film layers by SNMS/HFM method

Depth profiles of Ga₂O₃/a-SiO₂/Al₂O₃- substrate, Ga₂O₃/a-Si₃N₄/Al₂O₃- substrate, and Ga₂O₃/Al₂O₃ substrate thin layers were determined by the SNMS/HFM method. Al diffusion from the Al₂O₃ substrate was investigated after 50, and in some cases after 600 hours of heat treatment time at different temperatures (600 °C,850 °C,950 °C,1050 °C and 1150 °C). The diffusion coefficient of Al at 850 °C was found to be D _Al=8.7 * 10^–18 cm²/s in amorphous SiO₂; D _Al=1.5*10^–17 cm²/s in amorphous Si₃N₄ and D _Al=5.5* 10^–16 cm²/s in Ga₂O₃ at 600 °C, respectively. The possible diffusion mechanism is explained in terms of the metal-oxygen bond-strengths. Although the studied materials have high resistivity at room temperature, the applied SNMS/HFM method has proven to be an efficient surface analytical tool even in these cases.Dedicated to Professor Dr. rer. nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthday     

Solvent extraction of H3O+, NH4+, Ag+, K+, Rb+ and Tl+ into nitrobenzene by using cesium dicarbollylcobaltate in the presence of a hexaarylbenzene-based receptor

From extraction experiments and γ-activity measurements, the extraction constants corresponding to the general equilibrium M⁺(aq) + 1·Cs⁺(nb) \rightleftarrows \rightleftarrows 1·M⁺(nb) + Cs⁺(aq) taking part in the two-phase water–nitrobenzene system (1 = hexaarylbenzene-based receptor; M⁺ = H₃O⁺, NH₄ ⁺, Ag⁺, K⁺, Rb⁺, Tl⁺; aq = aqueous phase, nb = nitrobenzene phase) were evaluated. Furthermore, the stability constants of the ML⁺ complex species in nitrobenzene saturated with water were calculated; they were found to increase in the series of Rb⁺ < K⁺ < Ag⁺, Tl⁺ < H₃O⁺, NH₄ ⁺.     

Thermal analysis of nickel oxide films

Nickel oxide films were prepared by chemical deposition on glass substrates using nickel sulphate and potassium persulphate in ammonia solution. Coatings dried in air and at 85°C were characterized by thermal analysis (TG and DTG), FT-IR spectroscopy and X-ray diffraction. The films could be formulated as hydrated forms of 4Ni(OH)₂·NiOOH and Ni₃O₂(OH)₄ respectively. The coatings lost water and oxygen on heating to give NiO.